Calcium control in crystallization of sodium sesquicarbonate

Claim 1

A PROCESS FOR PREPARING CRYSTALS OF SODIUM SESQUICARBONATE FROM CRUDE GREEN RIVER, WYOMING TRONA, WHICH CRYSTALS ARE IMPROVED IN SIZE, CLARITY, DEWATERABILITY AND SETTLING RATE, WHICH COMPRISES SOFTENING THE NATURAL HARD WATER OF THE REGION, CONTAINING AN AVERAGE TOTAL HARDNESS OF ABOUT 85 TO 120 PPM. CALCULATED AS CALCIUM TO A CALCIUM HARDNESS OF LESS THAN 300 PPM. TO PROVIDE MAKE-UP WATER FOR SAID PROCESS, ADDING SAID MAKE-UP WATER SOFTENED TO A CALCIUM HARDNESS OF LESS THAN 30 PPM. CALCULATED AS CALCIUM TO A RECYCLING MOTHER LIQUOR CONTAINING PRIMARILY WATER AND DISSOLVED SODIUM CARBONATE AND SODIUM BICARBONATE TO PROVIDE A DISSOLVER FEED SOLUTION HAVING LESS THAN 30 PPM. CALCIUM HARDNESS, DISSOLVING, SAID CRUDE TRONA IN SAID RECYCLING MOTHER LIQUOR TO PROVIDE A DISSOLVER DISCHARGE SOLUTION HAVING LESS THAN 40 PPM. CALCIUM HARDNESS, CLARIFYING SAID SOLUTION TO REMOVE INSOLUBLES THEREFROM AND PROVIDE A CRYSTALLIZER FEED LIQUOR, MAINTAINING A CALCIUM CONCENTRATION IN SAID CRYSTALLIZER FEED LIQUOR OF LESS THAN 40 PPM., ADDING AN ANIONIC-ACTIVE SURFACTANT CRYSTALLIZATION MODIFIER TO SAID SOLUTION IN THE AMOUNT OF ABOUT 5 TO ABOUT 100 PPM., PRECIPITATING AND REMOVING SODIUM SESQUICARBONATE CRYSTALS FROM SAID SOLUTION AND RECYCLING THE MOTHER LIQUOR FROM THE CRYSTAL REMOVAL STEP TO DISSOLVE MORE TRONA.